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Appendix 3 - E-DBA Throughput/Latency Measurements Methods
The contents of this appendix are also available in Technical Instruction Sheet 044 (TIS044), dated
March 01, 2006.
Overview
The instructions in TIS044, intended for end-users, discuss the effectiveness of TCP/IP troubleshooting
tools in E-DBA networks. It shows how to assess network performance in the E-DBA environment. It is
reproduced here to complement the information given in section 5.4.
Performance Metrics
The following metrics are typically used to measure communication network performance:
♦
Latency
Also called “Response Time”. In this context, latency measures the amount of
time it takes for a response to return from a request. It takes into account the de-
lays accumulated at every step of the round trip.
Usually expressed in seconds or milliseconds.
♦
Throughput
The amount of information that can be transferred over a connection in a given
period of time.
Usually expressed in bits per second (bps), bytes per second (Bps) or packets per
seconds (pps)
E-DBA Primer
E-DBA is a
scheduled air-link protocol
whose algorithms were designed to favor throughput over la-
tency. To achieve that goal, the air-link uses adaptive timeslots called
cycles
to schedule traffic. These
cycles dynamically vary in length (typically, between 200 to 1500 milliseconds) based on various factors,
including network load.
Each packet of data transiting through an E-DBA network must therefore be scheduled for transmission,
which introduces a
scheduling latency
of one or more cycles.
PING as a Performance Measuring Tool
Ping is a utility used to determine whether a particular IP address is reachable by sending out a packet and
waiting for a response. It is therefore a good tool to measure network latency.
Because of E-DBA’s cycle mechanism, a ping packet could take up to 3 cycles to make the round trip,
producing an unexpectedly large ping time even when the radio channel is lightly loaded. For this reason,
Dataradio recommends that ping should only be used to verify if a device is reachable, not as a measure
of network performance.
On Ethernet-only networks, ping is normally set to timeout its request packets after 1 or 2 seconds. When
using ping over an E-DBA network, Dataradio recommends setting the ping timeout to 5000 milliseconds
or more.